1. Field of the Invention
The present invention relates to a reformer for obtaining a hydrogen-containing gas from a raw material gas such as a natural gas. Particularly, the present invention relates to a reformer for obtaining a hydrogen-containing gas by reacting a raw material gas to be reformed, with an oxidizing agent gas and a reforming agent gas. The hydrogen-containing gas thus obtained may be utilized, for example, as a fuel for a fuel cell or as a synthetic gas which is a raw material for synthesis of methanol, ammonia, hydrocarbon oil or hydrocarbons.
2. Discussion of the Background
As a process for producing a hydrogen-containing gas, there are well known a steam reforming process in which steam is used as a reforming agent for reforming a raw hydrocarbon material such as a natural gas, and a partial oxidation process in which a raw hydrocarbon material, such as a natural gas, and an oxidizing agent, such as oxygen, oxygen-enriched air and air, are used.
Referring to FIG. 2, there is explained a process for producing a hydrogen-containing gas using a steam reformer of internal heating type, wherein a raw material natural gas is reacted with an oxidizing agent gas and a reforming agent gas to obtain a hydrogen-containing gas.
Reactor 111 is constituted by combustion zone 121 equipped with burner 112, which is provided at the upper portion of the reactor, and reforming zone 122 filled with a steam reforming catalyst, which is provided at the lower portion of the reactor. The inside of reactor 111 is lined with refractory 113 such as brick for resistance to a high-temperature flame. Mixed gas 101 of a natural gas and a reforming agent gas is mixed with oxidizing agent 102 such as air at burner 112, and part of the natural gas is partially combusted. The heat generated by this combustion gives rise to a steam reforming reaction between the hydrocarbons in the remaining natural gas and the reforming agent gas during their passage through reforming zone 122; thereby, hydrogen-containing gas 103 composed mainly of hydrogen and carbon monoxide is produced.
In the above partial combustion, a flame is formed. When the flame contacts with the catalyst of reforming zone 122 at the lower portion of the reactor, a temperature of as high as one thousand and several hundreds centigrade is reached and the catalyst is melt; as a result, phenomena such as decrease in catalyst activity appear. Therefore, various proposals have been made to avoid such problems.
For solving the above problems, JP-A-2000-319006 discloses a technique for making uniform the temperature of the catalyst layer. This document discloses a fuel reforming apparatus for forming a hydrogen-containing gas, wherein a gaseous mixture of a fuel gas, steam and an oxygen-containing gas is introduced into a reactor having a catalyst filled in its upstream side and another catalyst filled in its downstream side to form a hydrogen-containing gas.
In this apparatus, there is provided, in a part of the catalyst layer at the upstream side of the reactor, non-contact passages in which the gas introduced makes no contact with the catalyst. In this structure, the gaseous mixture of a fuel gas, steam and an oxygen-containing gas, fed into the catalyst layer at the upstream side of the reactor forms a high-temperature zone; meanwhile, the gaseous mixture passing through the non-contact passages makes no direct contact with the high-temperature zone, but contacts the high-temperature zone via the walls of the non-contact passages and reaches the catalyst layer at the downstream side of the reactor.
As a result, the gas passing through the non-contact passages is exposed to a high temperature. Since this gaseous mixture contains oxygen, it is highly possible that the gaseous mixture forms a detonating gas depending upon the case.
Further, JP-A-2003-112903 discloses a small-sized fuel reformer in which the heat generated in a combustion catalyst part is transferred efficiently to a stream reforming catalyst part and thereby the generation of a reformed gas at the stream reforming part is enhanced.
In the above fuel reformer, the interface between the combustion catalyst part and the steam reforming catalyst part is formed in such a conical shape that the axial direction dimension (height) of the vertical cross section of the steam reforming catalyst part is made gradually smaller as the position of the height shifts from the periphery of the vertical cross section to its center; the reaction heat generated in the combustion catalyst part can be transferred to the steam reforming catalyst part more efficiently; and the formation of reformed gas is enhanced.